CHAPTER VIII. 

 ANALYSIS OF HETEROGENEITY IN COMPLEX CHARACTERS. 



COMPOSITION AND MODIFICATION OF THE PRONOTAL PATTERN. 



The pronotal color-pattern of this group, the genus leptinotarsa, affords an 

 opportunity for the investigation of heterogeneity in a highly " variable " 

 organic " character." The species as a rule are narrowly limited in distri- 

 bution, and some show minor habitudinal divisions. Within their habitats they 

 live in restricted colonies, as described in Chapter II, and are, therefore, localized 

 in differing habitats between which there is little interchange of populations. 

 These conditions produce isolated populations in which it is possible to test 

 some of the relations between the " variation " phenomena and the conditions of 

 existence. The pronotal color-pattern is chosen as a subject of observation 

 because of its composition of exactly localized elements and the ease with which 

 differences may be estimated, seriated, and recorded. It is a complex of simplest 

 characters, some of whose departures have already been analyzed. The pattern 

 of this part may be considered as a system largely independent of any of the 

 other parts. 



IN LEPTINOTARSA MULTlTitNIATA. 



In species like L. muUitceniata, examination of a collection of a thousand or 

 more individuals, taken at random over its geographical range, shows a wide 

 range of pronotal pattern, as shown in figure 34. Conditions from a totally 



Fig. 34. — Showing great diversity in color-pattern in L. multitcBniata through- 

 out Its range. The first appearance of these patterns on inspection would seem 

 to warrant the view that their aspects were entirely without order or uniformity. 



black surface to one with only the simple spots present are found, and between 

 these are all sorts of patterns, of differing amounts of pigment, and differing 

 combinations between the elements. In a given generation in some locations in 

 a large sample it is possible to find all or nearly all of the variations shown, while 

 in other locations and generations only a few are present. The treatment of a 

 population showing a character of this diversity depends largely upon the point 

 of view and the philosophical background applied to the problem. 



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